The ocean contains half the fish it had 50 years ago

There's a new study of Earth's marine life that suggests the ocean has gotten alarmingly roomy. To put a finer point on it, there are half as many fish in the sea today as there were in 1970, according to the World Wildlife Fund's "Living Blue Planet Report."Altogether, the study tracked 5,829 populations of 1,234 marine species, but the researchers behind it were especially concerned about the plummeting numbers of both mackerel and blue and yellowfin tuna, a fish prized by sushi lovers. Given these particular shortages, it isn't surprising to learn that while there are technically a lot of factors behind the dramatic drop — climate change, mangrove deforestation, an island of plastic floating in the Pacific the size of Texas — the biggest one is overfishing.

Researchers with the Zoological Society of London note that the global populations of fish in the delicious Scombridae family (tunas, mackerels, and bonitos) fell by about 75 percent over that time period. Ken Norris, a scientist with the Zoological Society, notes it's clear that "billions of animals have been lost from the world's oceans in my lifetime alone," and that, he adds, is "a terrible and dangerous legacy to leave to our grandchildren."